1. Technical Field
This invention relates generally to a method for forming open-celled cores for structural panels, and more particularly to such a method in which the cores are formed of segments of thermoplastic tubes.
2. Background Art
Several methods have been proposed for the production of open-celled cores, also commonly referred to as cellular or honeycomb cores, for structural panels. Generally, the prior methods have involved assembling a bundle of preformed tubes, sheets, or other individual components, horizontally and then while the individual tubes are restrained either adhesively or within a press or containment fixture, cutting the horizontally disposed components transversely, in a vertical direction, to form individual cores having a desired thickness.
For example, U.S. Pat. 5,032,208 issued Jul. 16, 1991 to Horst Strauss for PROCESS FOR MANUFACTURING A BUNDLE OF TUBES, teaches a process whereby the tubes are horizontally disposed within a gutter having an open first end and a moveable wall at a second end. While horizontally restrained within the gutter, the tubes are pushed outwardly beyond the open first end by movement of the moveable wall and cut vertically to form cores having a desired thickness. A problem with this method, and other methods which vertically separate a bundle into separate cores, is that the separated core must be supported, during and after cutting, in some manner to prevent it from falling to a horizontal position and breaking. This is a serious problem when cutting large, individual cores from bulky and cumbersome bundles.
In other core fabrication processes, the individual tubes, or components, are preassembled into a unitary structure by the use of an adhesive material, such as glue disposed along the lengths of the individual tubes or segments. For example, U.S. Pat. 5,683,782 issued Nov. 4, 1997 to Ranier Duchene and titled PROCESS FOR PRODUCING OF A HONEYCOMB STRUCTURE AND HONEYCOMB STRUCTURE SO PRODUCED, describes a process using an adhesively active thermoplastic coating to promote bonding between individual honeycomb tubes. In a similar manner, U.S. Pat. 2,477,852 titled STRUCTURAL PANEL CONSTRUCTION, issued Aug. 2, 1949 to C. E. Bacon, describes a structural panel construction in which the individual tubes are assembled by an externally applied adhesive, or by a further curing operation in which fibrous material is impregnated with a partially reacted resinous substance. Operations which require precoating of the individual tubes add complexity, extra cost, and time to the manufacturing process, as well as introducing myriad problems with handling of the coated tubes to prevent premature bonding prior to a desired alignment. In other processes, in which tube bundles are not constrained within a pressure structure during cutting or preassembled into an adhesively joined structure prior to cutting, generally require some form of containment during the cutting operation. For example, Japanese Patent Publication 62-196430 published on Aug. 29, 1987, describes a process for fabricating shock absorber components in which circular bands are disposed around the periphery of a bundle of thermoplastic tubes prior to cutting the bundle in a vertical direction.
The present invention is directed at overcoming the problems set forth above. It is desirable to have a process for separating a preassembled bundle of tubes into individual cores without having the support and handling problems associated with vertical cutting and vertical core separation processes. It is also desirable to have such a process in which the individual tubes are preassembled into a consolidated unitary structure prior to separation into a desired number of core members.
In accordance with one aspect of the present invention, a method for forming a cellular core member includes forming a plurality of thermoplastic tubular segments having substantially equal lengths defined by spaced apart ends, each thermoplastic segment having a longitudinal axis extending along the length of the segment. The plurality of thermoplastic tubular segments are arranged in side-by-side relationship with the longitudinal axis of each segment disposed horizontally and the ends of the segments generally aligned in a respective common vertical plane. The respective ends of the horizontally disposed segments are thermally cut, and simultaneously fused together in a direction transverse to the longitudinal axis of the segments and in a plane parallel to the general common planar alignment of the ends of the tubes, thereby forming a consolidated unitary structure having a defined height and width and a thickness defined by the distance between the cut ends of the tubular segments. The consolidated unitary structure is then rotated to position whereat the tubular segments are oriented in a-vertical direction. The consolidated unitary structure, with vertically oriented tubular segments, is then moved in a horizontal direction relative to at least one thermal cutting device horizontally disposed at a predefined vertical position between the cut and fused ends of the tubular segments. The consolidated unitary structure is then cut by the thermal cutting device along a horizontal plane parallel to the defined height and width of the consolidated unitary structure with the cut ends of the tubular segments on each side of the cut made by the thermal cutting device being simultaneously fused together, thereby forming separate cores each having a thickness defined by the vertical position at which the horizontally disposed thermal cutting device is positioned.
Other aspects of the method for forming a cellular core member, in accordance with the present invention, include cutting the ends of the horizontally disposed segments in a plane parallel to the general alignment of the ends of the tubes, with a hot wire. In a similar manner, other features include the cutting of the consolidated unitary structure along a horizontal plane whereby separate cores are formed, with a hot wire. Other features include placing the consolidated unitary stricture on a horizontally disposed conveyor belt, after thermally cutting the ends of the horizontally disposed segments and rotating the resultant consolidated unitary structure to a position at which the tubular segments are oriented in a vertical direction. Another feature includes moving the conveyor belt relative to the horizontally disposed, vertically positioned, thermal cutting device.
Still other features of the method for forming a cellular core member, in accordance with the present invention, include wrapping the consolidated unitary structure with a plastic film around the vertically disposed periphery of the consolidated unitary structure prior to moving the unitary structure in a horizontal direction. Still other features include moving the consolidated unitary structure to a temporary storage location prior to moving the unitary structure in a horizontal direction and cutting the consolidated unitary structure along a horizontal plane and simultaneously fusing the cut ends of the tubular segments.
Additional features of the method for forming a cellular core member, in accordance with the present invention, include wrapping two or more consolidated unitary structures, having substantially equal widths and thicknesses, together with a plastic film around the vertically disposed external periphery of the multiple consolidated unitary structures, after rotating the consolidated unitary structures to vertically position the tubular segments, to form an integrated assembly of consolidated unitary structures having a length equal to the combined lengths of the individual consolidated unitary structures prior to moving the integrated assembly of consolidated unitary structures in a horizontal direction.